STUDIES ON THE BASIC CARBONATES OF NICKEL
Part IV: Preparation of Basic Nickel Carbbnates and their
Differential Thermal Analysis
R. M. MALLYAAND A. R. VASUDEVAMLJRTHY
(Deparrmenr of Inorganic and P!7?sical Chemistry, Indian Inrrifnfe of Science, Ban&ore-I2)
Received on September 16, 1960
Several ~amplesof basic nickel carbonate3 were prepared under different experimental conditions obtained by varying the ratio of reactants, temperature, mode
of precipitirtion and period OF agelng Three basic nickel carbonates of composiIron ZNiO.CO2 5H20 ; 3N10.C0~.68:0and 4Ni0.COs.7Hz0 were prepared at 25°C
by drying prccipitates over anhydrous calcium chloride and tujo others of composition ZNi0.C0..31110 and 4Xi0.C0z.5H10 by drying these samples further in
vacuo over phosphorus pentoxide A few samples of basic carbonatcs obtaimd at
97°C from boilins solutions had very small carbonate contents. Differential
thermal analysis of some of these samples showed that two endothermic reactions
take place on heating.tha samples at a uniform rate up to 600°C.
It has been reported earlier' t h a t three basic nickel carbonates o f cornpositions (in t h e wet conditions) corresponding t o 2NiO : COZ, 3 N i 0 : C 0 2 and
4NiO: C 0 2 a r e formed a t 25'~ when solutions of alkali carbonates and nickel
salt? a r e niixed i n different proportions. Thcse carbonates are thrown out from
solution as very gelatinous precipitates associated with a large a m o n n l of water.
Since thcse basic carbonates a r c intermediates in t h e preparation of activz
nickei catalysts it is o f considerable interest t o characterise t h e physical and
chemical natures of these precipitates and their decomposition products.
Several samples of basic nickel carbonates were prepared a t 2 5 O ~and a t
9 7 ' ~under varying conditions o f precipitation and their compositions determined by analysis. Their thermal behaviour was examined by subjecting some
of the samples to differential thermal analysis.
'
Rra:e~zt used :-Exactly 0.05 molar solutions of nickel sulphate, chloride
and nitrate and decinorrnal sodium and potassinm carbonates were prepared a n d
standardised a s dcscribcd earlier.'
Preparation of the Basic Carboriatcs :-The precipitations a t 2 5 ' ~ were
conducted in a five litre pyrex hcaker kept in a large water thermostat. To
one litrc of 0.05 molar nickel salt solution taken in the beaker, the requisite
87
amount of decinormal alkali carbonate solution corresponding t o a definite
molar ratio was added a t a fast dropwise rate from a dropping funnel. ~h~
solution was stirred mechanically during the addition of the reagent t o ensure
homogenous dispersion of the reactants. Otherwise it is not possible t o get a
precipitate of uniform composition under the heterogeneous conditions which
pcvail.' Immediately after the addition of the alkali carbonate was complete,
the precipitate n a s transferred on to a Buchner funnel t o drain off the mother
liquor under suction. The precipitate was transferred back to t h e beaker and
dispersed into four litres of distilled water by mechanical stirring. The solution
was allowed to stand and the supernatant liquid was drained off. The process
was repeated six times and the precipitate finally transferred o n to a large dish
kept in a desiccator through which carbondioxide-free air, dried over anhydrous
calcium chloride was passed. The wet precipitate (105 gms.) was dried in this
manner for nearly six weeks in which time it lost its waler gradually t o the
extent of about 9 5 % of its ipitial weight (final weight = 5.3 gms). The precipitate, which was dark green in colour when dried, was powdered in an agate
mortar and transferred t o a small petty dish. The process of drying was continued in the same way till constant weight was obtained. The basic nickel
carbonate was stored in a weighing bottle and preserved in a desiccator over
anhydrous calcium chloride. The powdered basic carbonate of nickel was
light green in colour and free Bowing.
Some samples of nickel carbonate were precipitated at 9 7 ' ~ . A calculated
quantity of alkali carbonate solution was run from a dropping funnel into a
boiling solution of 0.05 molar nickel salt solution. The contents were stirred
thoroughly during the addition. The temperature of the solution during the
addition was found t o be 97'f 1 ' ~ . Immediately after the addition was complete, the solution was transferred into a Buchner funnel and filtered under
suction. The precipitate was freed from ions by washing it with cold distilled
water in some cases and in others by washing with hot distilled water. The
precipitate was then transferred t o a dish and dried in air over anhydrous
calcium chloride as in the previous set of experiments. The precipitates were
formed as greenish white brittle flakes.
Analysis o f the dry precipitates :-The various samples of dry basic nickel
carbonates were analysed For their water, carbondioxide and nickel oxide
contents gravimetrically. A weighed amount of the sample contained in a
porcelain boat was kept in a horizontal hard glass combustion tube and heated
to 500'C at a slow rate in a tubular electric furnace. The gases evolved were
swept by a current of pure and dry (freed from carbondioxide and water by
bubbling through caustic potash and concentrated sulphuric acid) nitrogen into
a series of three clean, weighed U-tubes. The first contained anhydrous
magnesium perchlorate t o absorb water and the second ascarite for absorption
of carbondioxide. The third U-tube again contained anhydrous magnesium
perchlorate to absorb any water given off by ascarite? The gas was then
passed through a guard U-Lube coi~tuining anhydrous calciuin chloride and
through a bubbler containing barium hydroxide solution. This served to in&care that t h e absorption of carbondioxide was complete. When the sample
bad been healed u p t o SOO"C, the furnace was switched off and the current of
nitrugell was continued for half a n hour m o r z The assembly was then disconnected. T h e porcelain boat and t h e U-tubes were transferred t o a desiccator
and weighed. T h e incre:ise in weight of the first U-tube gives the amount of
water absorbed a n d t h a t of the second and third U-tubes the net amount of
carbondioxide absorbed. The necessary blank correctipns were made and a
special method o f weighing t h e U-tubes was employed as described below. The
residue in the boat was nickel oxide and its nickel content was confirmed by
dissolving t h e residue in dilute (1 : 1) hydrochloric acid and determining the
nickel content gravimetrically by the dimethylglyoxine method. T h e results
were expressed t o give t h e composition of t h e precipitates in term? of the nickel
oxide, carbon dioxide and water conlents.
Y~ocedureadopted for weighing rhe ~ - t u b p s:-Considerable
diniculty was
experienced initially in the determination of the exact weights of the U-tubes
with contcntents. Dcpcnding upon the atn~osphericconditions and the interval
of time for which the U-tubes werc cxposed to laboratory conditions, differenceq
in the weights of the U-tubes were recorded even when counterpoi~edsuitahly.
These difiererices could not be ndequntely accounted for hy applying corrections
for the tempzrature changes a n d buoyancy effects. Aftcr a number of attempts
to standardise the weighing process, it was concluded that the diKcrence observed
was chiefly due t o [he different weights of the film of water adsorbed a t the
glass surface. It was therefore neiessary t o subject the U-tubes t o the saniz
uniform treatment prior t o each weighing. Such a a treatment was given in a
satisfactory manner as follows.
A piece of muslin was washed with water and
then squeezed t o remove all droplets of water from it. Before weighing the
U-tube each time, it was first wiped with this moist muslin and then immediately
with a dry piece of muslin. T h e U-tube was then suspended in the balance pan
for exactly 15 minutes and then weighed. In this manner t h e weighings could
be reproduced t o +0.0001g.
Blank correction :-In
order t o upply corrections for t b r moisture and
carbon dioxide adsorbed within the apparatus and which are liberated during
the experiments, blank experiments were run in exactly t h e same manner a s
described above, hut with an empty porcelai~lboat. There were slight increases
in the weights of the first and second U-tubes but none in t h e third. The mean
amounts of water a n d carbondioxide absorbed in t h e U-tubes during any
deterininalion were 1.9 mg. and 0.1 mg. respectively. The corresponding
Corrections were therefore applied t o each experimental result.
T h e p r o c e d ~ ~ rdescribed
e
above was applied to t h e determination of water
and/or carbondioxide in standards like sodium bicarbonate, magnesium sulphate
R. M. MALLYAAND A. R.VASUDEVA
MURTHY
90
heptahydrate and magnesium carbonate. When the necessary blank corrociions
were applied, the results were in close agreement (Ivithin 0.4 per cent) with the
theoretical values.
RESULTS
-
The analysis of the various samples of basic nickel carbonates prepared at
molar ratios of reactants alkali carbonate/nickel salt 1.0, 1.5 and 3 0 under
different conditions at 2 5 k and 9 7 ' ~are presented in Tables I and Il respectively.
TABLE1
Analysis of Basic Nickel carbonates oblained
a t 25°C
--.
Am,, of ppt,
Amount Found (.T)
System
A.
taken (g)
N~O
Reagent Ratio M2co3/iYi salt
-
-- .- -Ralio by weight
N i 0 : C 0 2: H>O
HnO
- ---. - - - .
.- - --
-
.
..
1.0
[I] Unaged Ppt. Dried over anhydrous CaC12
0.1678
0.0884
0.0261
(b) N i ( ~ 0 , ) ~Na2C03 0.1594
0.0840
0.0320
0.0247
0.0094
(a) NiS04 -Na,C03
(c) NiC12 -Na,COI
-
( d ) NiSOo K2C03
0.0532
3.39 : 1.00: 2.04
0.0505 3.40 : 1.OO :2.04
0.0610
0.0192 3 41 : 1.00: 2.03
0.0956
0.0508
0.0147
0.0302 3.43 : 1.00 :2.06
Compn. 2Ni0.C02-5H,O corresponds to 3.394 : 1 00 : 2.046
[It] Unaged ppt. dried in vacuo over P20S
( a ) NiS04 -Na2C03
0.0888
0.0734
0.0526
0.0439
0.0161
0.0199 3.41 : 1 00: 1.23
0.0132
0.0162 3.40 : 1.00: 1.22
The composition 2Ni0.C02.3H20 corresponds to 3.394: 1.00: 1.228
( b ) NiSO4 -K2C0,
[TII] Precipitate aged for 4 hours with agitation dried over anhydrous CaC1,
(a) NiS04 -Na2C03
0.8075
0.0640
0.0126
0.0309 5.08 : 1.00: 2.45
(6) NiCI2- Na,CO,
0.1258
0.0748
0.0147
0.0361 5.09 : 1.00: 2.46
(c)
N~(SO&- K,CO,
0.1685
0.0998
0.0196
0.0486
5.09 : 1.00 : 2.48
B. Reagent ratio M$o,/N~ Salt = 1.50 (1 hour's agitation)
ppt. dried over anhydrous CaCI,
(a) NiS04 -Na2C03
0.1018
(c)
0.0601
0.0634
0.0118
0.0291
0.0124
0.0305
N i ( ~ 0 ~ )&CO,
~0.1420
0.0925
0.0144
0.0350
The composition 3Ni0.C02.6H20 corresponds to
( b ) k i c ~ z - ~ a , ~ ~ 0.1066
p
.
~~
-
5.09
5.19
5.10
5.091
. ... .
: 1.00: 2.47
: 1.00:2.46
: 1.00: 2.43
: 1.00:2.456
-...
- --
Studies on the Baric Carbonates of Nickel
91
System
C. Reagent ratio M2C03/Nt salt
-
3.0
[I] Unaged ppt. dried over CaCI2
(a) NiS04 - NazCOj
0.1364
(b) N ~ ( N o ~ )-, Wa2C03 0.1664
(c) NiCIz
- NazCO,
( d ) NiS04 - 1<zCo3
-
(e) NI(NO,), K2COJ
( f ) NiCI2 - K2COs
0.0869
0.1251
0.0128
0.0365
0.0184
0.0528
0.0315
0.1173
0.0748
0.1834
0.1 169
0.01 10
0.0172
0.1321
0.1710
0.0835
0.i096
0.0123
0.0161
0.0492
0.0353
0.0461
[II] Precipitate aged for 10 days dried over CaCI,
(a) NiS04-Na2C03
0.1216
0.0773
0.01 14
0.0327 6.78 :1.00: 2.87
(b) NiC1,Na2CO3
0.1090
0.0694
0.0102
0.0291 6.80 : 1.00: 2.85
The composition 4Ni0.C02.7H20 corresponds to 6.787 : 1.00 :'2.865
[III] Precipitate dried in Vacuum over PzOr
0.1264
(a) NiS04-Na2C03
0.0872
0.0129
0.0262 6.76 :1.00:2.03
0.1048
(b) NiC1,-Na2C03
0.0723
0.0107
0.0217 6.76 : 1.00 :2.03
The composition 4Ni0.C02.5HZ0 corresponds t o 6.787 : 1.00 :2.046
.
.. .
--- .
- .. - -- --- -. - -- - -The precipitate obtained when a nickel salt solution is treated with an
equivalent amount of alkali carbonate solution at 2 5 O ~has a composition
2Ni0.C02.5H20 when dried in air over anhydrous calcium chloride. It is
immaterial whether a chloride, nitrate or sulphate salt of nickel is used for the
purpose of precipitation. If this same precipitate is subjected to further desiccation in vacuum over phosphorus pentoxide it loses some of it3 water content and
approaches slowly the composition 2Ni0.COZ.3H20. If the wet precipitate is
allowed to remain with the mother liquor for a longer interval (about 4 hours
with agitation) the final composition of the aged precipitate, when dried over
anhydrous calciunl chloride, corresponds t o 3Ni0.C0,.6B20. A precipitate
with the same composition can also be obtained if the alkali carbonate added
is 1.5 times the molar content of the nickel salt taken. Ageing has no perceptible effect on the composition of this precipitate which is consequently a more
stable composition. If the alkali carbonate added is three times the amount
R. M. MALLYAAND A. R. VASUDEVAMURTHI
92
TBALE11
Analysis of basx nxckel carbonates plepared at 97°C
-
__
-
-
-- --
-
-
-.-
-
-
A. Reagent Ratio M,CO,/N~ salt = 1.0
[I] Precipitate washed with cold water
( a ) NiS04-Na2C03
0.1074
0.0810
0.0034
(b) NiC12-Na2C03
0.1756
0.1331
0.0055
[II] Precipitate washed with hot water
( a ) NiS04-Na,COj
0.1257
0.1005
0.0037
(b) NiS04-KKO,
0.1384
0.1106
0.0041
B. Reagent Ratio M , C O ~ / N ~salt = 3.0
[I] Precipitate washed with cold water
(a) NiS04-Na2C03
0.1458
0.1099
0.0038
(b) NiC12-Na,CO,
0.1677
0.1253
0.0042
( c ) NiS04-K2C03
0.1193
0.0865
0.0031
[II] Precipitate washed with hot water
(a) NiS0,-Na,COj
0.0915
0.0748
0.0021
( b ) NiS04-K2C03
0.1526
0.1244
0.0034
of nickel salt taken, the composition of the precipitate after drying over anhydrous calcium chloride is found to be 4Ni0.C02-7H20. Ageing and stirring
have no influence on the composition of this precipitate. The same composition of the precipitate is obtaincd a t this molar ratio of reactants irrespective
of the nickel salt used.
II the precipitation is carried out at 9 7 ' ~and the reactants are used in
equimolar proportions, the carbonate content of the precipitate is very much
decreased. The composition of the precipitate when washed with cold water
and dried over anhydrous calcium chloride is nearly 14 Ni0.C02.16H,0. When
the precipitate is washed with hot water there is a further decrease in the water
and carbondioxide contents of the precipitate. The composition of the precipitate is around 16Ni0.C02.15H20. Similar observations are made when cxcess
of alkali carbonate is used for precipitation. Considerable variation is observed
in the results depending on the manner and extent of washing.
Stun'ies on the Basic Cmbonafes nf Nickel
93
The precipitates obtained from boilins solutions are pale, whitish-green,
crystals, which when dried are easily powdered by pressing with a spatula.
On the other hand, the precipitates obtained a t 2 5 ' ~are dark green and gelatinous and contract to a hard mass on drying. This can be powdered only in
~
down very easiiy
an agate mortar. The precipitates obtained a t 9 7 O settle
and are also easy to wash. However, on washing with cold water, the supernatant layer becomes slightly turbid indicating that the precipitate is broken
up into particles of collodial dimensions. This peculiar behaviour exhibited
by these basic salts may be explained on the mode of precipitation and its
mechanism which are discussed at a later stage in this series." Such an effect,
was notobserved when hot water was used for washing.
heavy
D$ferential thermal analpis of the basic nickel carbonate :-The
metalic carbonates are relatively unstable at higher temperatures where the
corresponding carbonates of the alkali metals are stable. Most of the normal
metallic carbonates decompose giving rise to the corresponding oxide and carbon
dioxide. The nature of the oxide lefl behind is of interesl since it plays a role
in such properties of the oxides as its influence on the course of reactions when
it functions as a catalyst. The thermal decomposition of basic nickel carbonates is of great interest since several important nickel catalysts are prepared by
decomposition of these basic carbonates and the subsequent reduction of the
product. The differential thermal analysis of representative samples of basic
nickel carbonate was thcrefore undertaken."
'
Apparatus :--The apparatus for differential thermal analysis comprised of
a tubular furnace constructed by winding SWG 24 nichrome wire on a silica
(or alundum), tube (2.3" diameter) and lagged with magnesia-asbestos powder.
The furnace was mounted vertically. A cylindrical nickel block with two
symmetrical parallel holes was used as the specimen holder and mounted snitably on a vertical, movable, rerractary support. Two chroniel-alumel thermocouples, conuected in opposition to each other were fixed, each a t the centre
of one hole and th? terminals were maintained a t 0 ° C in a bath of melting ice.
The temperature of the furnace was measured by means of a Leeds and Northrup
potentiometric unit (No. 248224) standardised against the standard Weston
Cadmium Cell. The differential temperature was noled by means o f a highsensitive, D'Arsonval moving coil galvanometer (Leeds and Northrup, sensitivity = 0 0003 irc/mrn) with a lamp and scale arrangement. The furnace wcis
heated a t a unif'orm rale manually with the help of a ' variac '.
Procedzrre;-One of the holes of the sample block was packed tightly with
freshly ignited alumina which served as the inert reference material. The
powdered sample of basic nickel carbonate .was similarly packed into the other
hole. The furnace was heated uniformly a t a rate of 1 2 ' ~per minute and at
various intervals the differential shift and the temperature at which i t occurs
were noted.
Results:-The
differential thermal analyses of several samp!es of basic
nickel carbonates of composition 2Ni0.C02.5H20 and 4NiO.C0y7H2O prepared
as described earlier in this paper, was conducted. The results with some
representative samples are shown in Figures I and 11.
TEMPERATURE
C
FIG.I
Differential thermal analysis of basic nickel carbonate 2Ni0.C0,.5Hz0
The results show that the decomposition consists of a two stage process.
In the decomposition of both the carbonates, the minima obtained in the
differential thermal curves indicate that both the reactions occurring are accompanied by the absorption of energy. The first peak is less endothermic than
the second. The peak temperature corresponding to the first decomposition i s
about 1 3 0 ' ~and that of the second is about 3 2 0 ' ~ . The first endothermic
peak corresponds t o the expulsion of part of the water and the second to that
Studies on the Basic Caiborinfes of A'ickel
95
o f the rest o f the w a t e r c o n t e n t and a l s o of cnrhondioxide.
T l ~ e i coixervntions are s u p p o r t e d fully by t h e r e s ~ i l t sof t h c r m o g r a v i ~ n e t ~ayn d m d y s i s of ~ 1
p r o d u c t s o f d c m n p o s i t i o n s t the corresponding slnges. 'I.
The
authors
t h a n k Prof.
R. R.
R r i s l ~ n n s w s n i ia n d
Prof.
M. K. A.
R a o for
their keen interest in t h e present work.
1. Msllga, R. M, and V a s d e v a Miirrhy,
A. R .
9
.
- ---
-
.
3. Hillcbrand, W. I:., Lundcll, G. E. F.,
Bright, 11. A. and Hoffman. J . 1.
4. Mnliya. R M. and Vasudeva Mdrthy,
..
..
..
h i d , 1461, 43, 41.
..
I . h i i o n Irirt. Sci., IYGI, 43 (Part \'I : to bc
published)
A. R.
-_
J. Indin11Inw. Sci , 1% I, .11, 65.
Inorganic Analysis ", I W ? , 2nd
Edn., 44-51 (Ncw York : Wilcy)
" Apphed
6 . Gray, T.J.
..
..
"
7. Smo~hers,W.J. and Chlaha, l'ao
..
" Differential Thermal Analysis - Theory
.
-
]bid, 19G1. 43 [Part V : to be published)
The Defect Solid State ", 19.57, 457-476
(New Yaik : lnterscience Publishers)
and Prnctice ", 1958, 21-77 ( N e w I'ork :
Chemic:il Publisling Co.)
, ~